thats just avast being avast. it is very overly protective and hates niche and not widely known exe files (such as indi games). I would recommend switching to using just windows defender as it will eat less resources on your computer
Just to check I ran the game's files through VirusTotal and all of them return as clear. I doubt that there would be a virus in this page's download. If you're still worried you can check yourself with VirusTotal or maybe download MalwareBytes or Hitmanpro and scan it.
